Over the past four decades, approximately 40 new pathogens have been identified. One of which (Legionnaire�s Disease) was identified during a major pneumonia outbreak in members of the American Legion attending the annual meeting in 1976 in Philadelphia. The incidence of Legionnaires� disease in the United States rose from 3.9 cases per million people in 2000 to 11.5 cases per million people in 2009, an increase of 192%. The increase might probably be attributable to increase proportion of elderly population who are more prone to acquiring infectious disease and developing life threatening complications. In addition, improvement in the healthcare in the United States has caused an increase in the number of immune-deficient individuals, such as cancer survivors, transplant patients or people on immune-suppressive medications for long term auto-immune diseases.

The episodes of Legionnaire�s disease showed some seasonal variation; 62% of the cases occurred during the summer and early autumn. The yearly incidence of this disease appeared to also be associated with climate changes, such as increased precipitation. Prior to 2015, only 24% of cases were travel-associated and 4% possible cluster. However, in 2015 clusters of cases, which exceeded all expectations, have occurred in states such as New York, Illinois, and California. The sudden change in the pattern of the Legionnaires� disease occurrence is not so clear to the scientist. Are these changes due to a change in our knowledge about transmission mechanism of Legionella bacteria or should we be worried about this agent being used in bioterrorism events? Or is the change artifactual and unreal?

Please answer the questions below in the order in which they are presented (see format for writing the comp exam). Be careful to align your answer with the case study as presented.

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A. Epidemiology and Biostatistics Section

Assuming you have conducted an investigation of the Legionnaire�s disease in a district in your locale and you have obtained the following data (the data is hypothetical), please use the data to:

i. Generate the descriptive summary statistics of the data.
ii. Draw an epidemic curve
iii. From your epidemic curve and your knowledge of the average and minimum incubation period for Legionnaire�s disease, identify the likely exposure period.

iv. Assuming you used a case-control study design to collect the data, describe in detail how you selected both cases and control groups. How would you ensure that your study is free of selection bias and information bias?

On the basis of your case-control studies, assuming you were able to find appropriate 54 controls for 27 of your cases as shown in the table below.

v. Using analytical epidemiology, determine quantitatively whether cases and controls were equally exposed to hot tubs.
Use appropriate statistical techniques to test the significance of your findings in question v

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